Not Applicable.
Not Applicable.
The present invention relates generally to inspecting objects, and more particularly, to automated optical inspection systems.
Automated optical inspection (AOI) systems are used to inspect objects, such as printed circuit boards (PCBs), for a variety of defects. The system can inspect a PCB for proper component presence and orientation, proper solder joint formation, and solder bridges. In one optical inspection application, a system can inspect the toe fillet solder joints of a quad flat pack (QFP) integrated circuit. Such a package has four edges with leads protruding from each edge. Each lead is connected to a pad on the PCB by a solder joint. An incorrectly formed solder fillet will have an appearance that can be detected using well-known image processing algorithms.
Such an AOI system includes a camera head that shuttles back and forth relative to the PCB. The camera head includes an illumination system and one or more cameras. The illumination system may be provided, for example, as one or more light emitting diodes (LEDs), which provide lighting for the purpose of highlighting certain surfaces on the PCB and darkening other surfaces on the PCB to allow the cameras to capture images that are amenable to image processing analysis. Typically, the lights are turned off and on only when the camera head is directly over a region or zone of interest on the PCB. Thus, the illumination system operates as a strobe light. With this strobe light approach, it is not necessary for the camera head to stop in order to acquire an image.
Typically, the board to be inspected is divided into stripes. Each stripe corresponds to a shuttle path along which the camera head travels. Each stripe is divided into fields of view (FOVs). As the camera head shuttles across various portions of the board, the illumination system strobes the lights in accordance with predetermined lighting modes to produce a flow of images from the cameras in the camera head. The images are transferred to memory via framegrabbers for analysis. Exemplary conventional automated optical inspection systems are disclosed in U.S. Pat. Nos. 5,260,779 and 5,260,779, both of which are incorporated herein by reference.
In addition to inspecting a fully assembled circuit board, an optical inspection system can inspect a board at various stages in the assembly process. In the automated manufacture of electronic circuit boards, there are several steps, each of which can be followed by an automated inspection step. The assembly line process can vary, but generally includes applying solder paste, populating the board with components, and heating the board to melt the solder.
Initially, an automatic stenciling machine, a discrete applicator, or other machinery well known in the art of electronic circuit board assembly places solder paste on a bare printed circuit board. The resultant board bears numerous dots of solder paste, which can be in the form of rectangular prisms known as xe2x80x9cbricks.xe2x80x9d The solder bricks can be inspected in a conventional manner to verify correct location and volume.
Another automated machine, such as a so-called chip-shooter or a pick and place machine, then places components on the board with the component electrical terminations or leads in contact with the bricks. The populated board can be inspected to verify that all components have been correctly positioned.
The board then passes through a heating system (e.g. a hot oven) to melt the solder bricks and form metallurgical bonds between the electrical terminations of the components and the plated metal pads of the printed circuit board. The assembled board can be inspected to verify that the solder joints are properly formed and that all components are still correctly placed.
One disadvantage associated with conventional optical inspection systems is the time and cost associated with the system learning the characteristics of new circuit board components. Before an optical inspection machine can inspect a particular type of board, the machine needs to learn the characteristics of each component on the board. Typically, the system is programmed in a manner that includes a xe2x80x9clearningxe2x80x9d step in which the inspection machine views each component and records digitized images of its appearance. These stored images, and/or attributes extracted from them, are used to generate models for the components against which the board components are compared while the machine inspects boards in a production environment.
As known to one of ordinary skill in the art, component learning can be a slow and burdensome process requiring fixturing (the fabrication of test fixtures), significant manual labor, and considerable time spent on the inspection machine itself. In addition, the inspection system is typically removed from the production inspection process to learn a new component. Thus, the whole assembly line must be stopped while the inspection system learns one or more new components thereby decreasing the overall production assembly efficiency.
It would, therefore, be desirable to provide an optical inspection system that reduces the time and cost associated with the inspection system learning the characteristics of new circuit board components. It would also be desirable to provide an inspection system that improves the overall efficiency of the inspection process on a production assembly line.
The present invention provides an automated optical inspection system that learns the characteristics of a new component as part of the overall inspection process. By integrating the component learning process into the inspection process, the overall inspection efficiency is enhanced. Although the invention is primarily shown and described in conjunction with an automated optical inspection system for printed circuit boards, it is understood that the invention is applicable to other inspection applications in which the characteristics of new components and objects need to be acquired from time to time.
In one aspect of the invention, an automated optical inspection (AOI) system for inspecting circuit boards includes a component learning area in which the characteristics of one or more components can be learned. In one embodiment, the component learning area is adjacent an inspection area in which the circuit boards are inspected. The component learning area can be imaged by one or more cameras used to provide images of the circuit board. The system integrates image acquisition of the circuit board with image acquisition of the new components so as to minimize the impact of the component learning process on the overall inspection process.
In an exemplary embodiment, the component learning area corresponds to a region that can be imaged by the camera(s) used to image the circuit board but is not used by the system for the inspection of boards. While the component learning area can be imaged by the camera(s), the camera support structure can prevent a board from reaching the component learning area. More particularly, the circuit board enters and exits the inspection area though passages defined by the system support structure, which can include pillars used to support the camera head assembly. The component learning area can be adjacent the inspection area and xe2x80x9cbehindxe2x80x9d the pillars, which is not accessible to the board.
In a further aspect of the invention, an automated optical inspection system receives requests for inspection of boards and learning of new components. The system determines opportune times for learning the new components during the board inspection process. Opportune times includes times during which boards are being loaded and unloaded, times at which camera path for inspecting the boards is proximate the component learning area, and times at which there are no board inspection requests. Opportunistic learning of new components minimizes, or eliminates, the impact of component learning on the overall board inspection process efficiency.